The long term objective of this research involves determining the mechanism whereby the mouse discs- large homolog 1 gene, Dlgh1, regulates urogenital development. DLGH1 is a scaffolding protein with multiple protein-protein interaction domains, including three PDZ domains and one SH3 domain. Dlgh1 is a homolog of the Drosophila discs-large gene, dlg, which is a founding member of the eponymous PDZ family of proteins and also of the MAGUK (membrane-associated guanylate kinase) family. Studies in Drosophila suggest that dlg is a tumor suppressor, because mutation of dlg causes overgrowth of imaginal discs. Studies in both fly and mammalian cells suggest that dlg and its homologs are also involved in establishing and/or maintaining epithelial cell polarity. We have studied mice lacking DLGH1 and found several urogenital defects, including sporadic renal agenesis, congenital hydronephrosis, and reproductive tract abnormalities. We have shown that hydronephrosis is associated with dramatic smooth muscle alignment defects;the normally circular muscle aberrantly aligns in the longitudinal direction. This greatly impairs the squeezing motion of peristalsis, such that urine is retained in the kidney. In addition, ureteric stromal cells, which normally lie between the urothelium and the smooth muscle layers and express Raldh2, are absent from Dlgh1 mutant ureters. The absence of these cells could also affect ureteric function, either directly or indirectly. Immunofluorescence studies show that DLGH1 is expressed strongly in the urothelium and weakly in other cells of the ureter. We will determine which cellular compartment must express Dlgh1 for normal smooth muscle cell alignment and for differentiation and/or migration of ureteric stromal cells using a new floxed Dlgh1 allele and appropriate Cre transgenic mice. In addition, we will generate chimeric mice to investigate whether DLGH1 acts in a non-cell autonomous fashion. Morphological and functional assessments will be performed to determine the cellular requirements for Dlgh1 expression. Next we will use genetic methods to investigate the hypothesis that the interaction of other DLGH family members with known or suspected DLGH1 binding proteins are compensating in part for the absence of DLGH1. Finally, we will use in vitro methods to define the role of DLGH1 in cell migration, polarization, and signaling. PUBLIC HEALTH RELEVANCE: Congenital urinary tract abnormalities are a relatively common health problem in the human population and are responsible for a significant number of cases of progressive renal disease. We have generated a novel mouse model of hydronephrosis (Dlgh1-/- mice) involving the misalignment of ureteric smooth muscle, which is commonly found in human cases of urinary tract obstruction. A better understanding of the biology of DLGH1 could have important implications for understanding and perhaps for treatment or prevention of urinary tract abnormalities in humans.